It is proposed to investigate the biogenesis of cellular membranes in a variety of cell types in which proliferation of membranous organelles takes place. Tissues for study include the livers of phenobarbital treated rats, alloxan diabetic rats and neonatal rats, the hepatocytes of which exhibit marked proliferation of smooth endoplasmic reticular membranes compared with control livers, the rat pancreas, the acinar cells of which show an increased formation of golgi membranes on stimulation of secretion, and the salt gland of the duckling, the secretory cells of which exhibit marked growth of plasma membranes in response to salt stress. Using both electron microscopy, including morphology and cytochemical approaches, and biochemical techniques, including cell fractionation, enzyme assays, and analyses of membrane components, it is proposed to investigate the site of synthesis of the phospholipids and marker enzymes of newly formed membranes, and to investigate the time course of incorporation and the site of assembly of these components into new membrane during proliferation. The phospholipid patterns of different membranes and the relationship of this to the increased specific activity of marker enzymes will also be investigated. On the basis of the results of these studies, investigations of the control of membrane biogenesis will be made. In initial studies actinomycin D, puromycin, and cycloheximide will be used to determine the possible involvement of mRNA synthesis or protein synthesis in the process. In addition, the role of non-genetic controls will be investigated, the individual experiments being dependent on the tissue studied and the stimulus of membrane proliferation.